This invention relates to blind rivets and to a method and apparatus for manufacture of blind rivets. Blind rivets have been produced in strips, with each rivet having a pin within a sleeve, with the rivet being fixed in placed by pulling the pin in the sleeve to expand the sleeve for fastening material between the expanded portion of the sleeve and the flange of the sleeve. Rivets of this type are shown in U.S. Pat. No. 4,222,304, and may be fixed in place by a pulling gun of the type shown in U.S. Pat. No. 4,131,009.
In the prior art rivet as shown in U.S. Pat. No. 4,222,304, a plurality of pins is molded in a first set of cavities. Then this set of pins is lifted from the first set of cavities and positioned in a second set of cavities where the sleeves are molded around the pins. Interconnecting strips are molded between the heads of the pins to provide the strip of rivets. This patent does not disclose any mechanism for moving the molded pins from the pin cavities to the sleeve cavities.
In the cavities, the individual pins are aligned with the individual sleeves, with the pin cavities being fed from a runner through the pulling head of the pin and with the sleeve cavities being fed from the tail end of the pin. With this configuration, there is a runner at each end of the finished rivets.
In another prior art arrangement, which does not appear to be the subject of an issued patent, the set of sleeve cavities is positioned in parallel with the set of pin cavities, with all cavities being fed from the tail ends through the same runner.
After a molding operation is completed, the mold members are opened and the molded strip is advanced along a path perpendicular to the individual cavities, with the molded pins being positioned in the sleeve cavities for the next molding operation of sleeves about the pins.
The molded strip is advanced by a reciprocating carrier which is positioned at the head end of the pin cavities, with the pin heads molded about a blade of the carrier which forms a dovetail groove in the pin heads.
This later prior art arrangement provides for automatic advance of the molded pins into the sleeve cavities and for formation of a continuous strip of molded rivets. However problems have been encountered in the use of this apparatus.
Accordingly, it is an object of the present invention to provide a new and improved blind rivet strip and method and apparatus for forming the blind rivet strip which will result in a less expensive and more reliable tool and one which is more easily maintained and which can be operated at higher production rates.
It is another object of the invention to configure the cavities, runners and material feeding sprue to reduce the amount of molding material that is wasted.
The utilization of the blade and the dovetail slot in the pin head for strip advance results in flash and debris in the slot, which causes undesirable material wear and jams in the pulling gun. Accordingly it is another object of the invention to provide an automatic molding apparatus and method which does not utilize a groove in the rivet pulling head.
Other objects, advantages, features and results will more fully appear in the course of the following description.